Asphalt compositions have been used in broad applications to road pavement, sound shielding sheets, and asphalt roofing. Such asphalt compositions have a variety of polymers added to provide the performance according to each application. For example, block copolymers of ethylene-vinyl acetate copolymers, ethylene-ethyl acrylate copolymers, rubber latex, and conjugated diene with vinyl aromatic hydrocarbons are added.
Recently, asphalt compositions having high strength, flow resistance, and wear resistance have been increasingly required with an increase in the number of vehicles running on roads or an increase in speed of vehicles. It is considered that asphalt compositions having higher softening points and enhanced mechanical strength such as elastic modulus are needed to satisfy these requirements, hence leading to attempts at improvement by increasing the molecular weights of the copolymers listed above.
Unfortunately, these asphalt compositions do not have sufficient performance in the storage stability during storage at high temperature. In addition, these asphalt compositions have high melt viscosities, resulting in inferior applicability during road pavement.
Because of these, the storage stability is improved through addition of aromatic oils, sulfur, or peroxide, followed by crosslinking.
For example, techniques using sulfur (for example, see Patent Literature 1), and those using sulfur and a vulcanizing agent in combination with a sulfur-containing vulcanization accelerator are disclosed (for example, see Patent Literature 2).
An asphalt composition comprising a copolymer composed of a conjugated diene having a specific structure and a vinyl aromatic hydrocarbon is disclosed (for example, see Patent Literature 3).
An asphalt composition for roofing shingles comprising a block copolymer composed of a vinyl aromatic hydrocarbon and a conjugated diene and a filler is disclosed (for example, see Patent Literature 4).
An asphalt composition comprising a block copolymer composed of a vinyl aromatic hydrocarbon and a conjugated diene and a hydrogenated copolymer having hydrogen added thereto is disclosed (for example, see Patent Literature 5).